Wind power plants or ‘wind farms’ generally comprise a number of wind turbines that are electrically connected together to form a collector grid. The output from this collector grid is typically connected to a substation, which includes a step-up transformer for increasing the voltage to a suitable level for supplying a distribution grid.
Each wind turbine in the collector grid includes its own step-up transformer, also referred to herein as the ‘main transformer’, which increases the voltage output from the wind turbine generator to a higher level for supplying the collector grid. Each wind turbine also includes switchgear such as a circuit breaker or a switch-fuse device for protecting the electrical equipment inside the wind turbine in the event of a fault condition. The switchgear generally also comprises one or more cable switching devices, which comprise disconnector switches, and which are associated with the incoming and/or outgoing cables of the collector grid. These so-called ‘disconnectors’ allow the wind turbine to be disconnected from the connector grid for servicing purposes or otherwise.
Switchgear equipment for wind turbines is generally in the form of ‘panels’. Typically there will be a circuit breaker panel, which is connected to the main transformer, and one or more ‘disconnector’ panels, also known as ‘cable panels’, which connect the wind turbine to the next wind turbine in the collector grid. In practice, the panels may also incorporate other protective devices including earthing switches and/or surge arrestors. The circuit breaker panel may also include a disconnector switch.
The various panels forming the switchgear are arranged side-by-side and connected together via direct busbar connections. The switchgear may be supplied as a compact unit in which the panels are already connected together in this way, or in the form of separate modules, which are connected together onsite via the integral busbars. In existing wind turbines, the switchgear is located inside the base of the wind turbine tower.
There is a continual drive to increase the size and output of wind turbines. In turn, the rated voltage level in wind farms has steadily increased over recent years. Voltage levels of 36, 40.5 kV and 72 kV are now envisaged for the future. Moving to higher voltages results in a necessary increase in the size of the wind turbine equipment such as the transformer, and also of the switchgear required to protect this equipment. Housing such large equipment within the confined space inside the wind turbine tower then becomes a challenge, and there is a need to develop innovative new ways of arranging the switchgear.
It is against this background that the present invention as been made.
According to the present invention there is provided a wind turbine comprising: a tower; a rotor supported at an upper end of the tower; a generator; a transformer for increasing the voltage output of the generator prior to supplying a collector grid; and switchgear arranged between the transformer and the collector grid, the switchgear comprising a first switching device associated with the transformer, and a second switching device associated with one or more cables connecting the wind turbine to another wind turbine in the collector grid, wherein the first switching device is connected to, but located remotely from, the second switching device.
By separating the switchgear into electrically connected devices that can be arranged at different physical locations within the vicinity of the wind turbine, the present invention provides increased flexibility in terms of locating the switchgear. For example, part of the switchgear may be located inside the tower and part of the switchgear may be located outside the tower. Alternatively, parts of the switchgear may be arranged at different locations within the tower. For example part of the switchgear may be located at the base of the tower, and another part may be located on a platform inside the tower. The various parts of the switchgear may be connected together by electrical cables. This provides a more flexible solution than the busbar connections in the prior art that require the switchgear panels to be located side-by-side and at the same physical location.
The first switching device preferably comprises a circuit breaker for protecting the transformer in the event of a fault condition such as a short-circuit, an over current or an earth fault (ground fault). The first switching device preferably also includes a disconnector switch connected in series with the circuit breaker. The first protection device is preferably in the form of a ‘circuit breaker panel’. The second switching device preferably comprises at least one disconnector associated with the incoming and/or the outgoing grid cables for connecting and disconnecting the wind turbine to/from the collector grid.
In a preferred embodiment of the present invention, the first switching device is located inside the tower and the second switching device is located outside the tower. Locating part of the switchgear outside the tower frees up space inside the tower for other equipment or otherwise increases the accessibility of the equipment inside the tower for service personnel. This becomes increasingly important as the physical size of the switchgear equipment increases to accommodate higher rated voltages.
The first switching device may be located at the base of the tower or on a platform above or below the base of the tower. The second switching device may be located on a platform outside the tower. The platform may be a gallery platform of the tower or part of a foundation on which the tower is supported, such as an offshore foundation. The foundation may include a transition piece upon which the tower stands, and the second switching device may be located within the transition piece. The second protection device may be pre-installed inside the transition piece, which facilitates installation because the second protection device may then be lifted onto the foundation with the transition piece and a separate lifting stage is then no required.
Most service operations on the switchgear are performed on the circuit breaker panel as opposed to the cable disconnector panels. It is therefore convenient to locate the circuit breaker panel inside the wind turbine where it will be in relatively close proximity to the other operating equipment of the wind turbine. This facilitates service operations. As disconnector panels require less frequent servicing, these can be located in less accessible space, or space remote from where the usual service operations take place, such as outside the wind turbine for example. In addition, most operations on the disconnector panels are performed remotely, typically via SCADA (supervisory control and data acquisition), and so the location of these components is less important than the location of the circuit breaker panel.
Preferably the first switching device is located adjacent the transformer. The first switching device may include additional protective equipment such as surge arrestors and it is desirable to have these as close to the transformer as possible. If the first switching device was located outside the wind turbine and connected to the transformer by a long cable, for example, this cable would be susceptible to lightning strikes. Whilst such lighting strikes are rare, locating the first switching device adjacent the transformer avoids this risk.
The second switching device may conveniently be located inside a container. If the container is to be located outside the tower, then a substantially weatherproof container may be employed. A number of advantages flow from having the switchgear equipment located in a container. For example the equipment inside the container can be connected together and tested before being installed on site. Various optional and advantageous features of the container, which are discussed below, facilitate quick and easy connection of the containerised equipment to the equipment inside the wind turbine and to the collector grid. In the event of a fault developing with the containerised equipment, the entire container can be replaced rather than replacing or repairing the equipment inside the container. The containerised equipment may subsequently be repaired offsite. This presents significant benefits, particularly in an offshore context where environmental conditions can be extreme and it is generally desirable to minimise service time onsite. Replacing the entire container also reduces the downtime of the wind turbine.
The present invention also provides, within the same inventive concept, a weatherproof container configured to house switchgear components for a wind turbine.
To facilitate connectivity of the containerised switchgear equipment, the container preferably includes at least one hatch for providing access to one or more cable connection points of the second switching device. The wind turbine cable and the incoming and outgoing grid cables connect to the respective connection points. The connection points preferably comprise sockets, and the ends of the cables are preferably fitted with complementary-shaped plug connectors allowing quick and easy connection to the sockets.
The or each hatch may be provided in the base of the container. So that the hatches are accessible, the container may be supported on the platform with its base raised above the platform. To this end, the container may be supported on legs or other such supports. The container may comprise retractable or detachable legs that can be retracted or detached for convenience during transport of the container and extended or attached on site to allow access to the hatches. Retractable legs could also be extended specifically to provide access to the hatches when required, with the legs remaining retracted at other times such that the base of the container is supported directly on the platform. Alternatively, the legs may be part of a platform on which the container is supported. This solution may be cheaper than integrating the legs with the container.
The container may have one or more doors or a removable panel, for example a removable side panel, to allow access to the containerised equipment for maintenance purposes. Bolts or other fasteners may be used to secure the side panel to the container, which could be removed or otherwise unfastened in order to remove the panel. Rather than being removable, the panel may alternatively slide sideways or lift upwards. Moving the panel in any of these ways provides service access to the containerised equipment when required and means that the service space does not need to be factored into the size of the container. Accordingly, a relatively small container may be used, just large enough to house the equipment, without the requirement for additional service space inside the container around the equipment.
If the container is to house just the disconnector equipment, it is possible to use a very small container, which advantageously may be substantially smaller than a standard shipping container. This again allows greater flexibility in terms of locating the container, and allows the container easily to fit within the transition piece of an offshore wind turbine. A small container is also less unsightly than, for example, a large shipping container located next to the wind turbine. The container may be substantially cubic, for example with a dimension of about 2 m3 or less. Alternatively, the container may be elongate and have approximate dimensions of 1.5×2×2.5 m (i.e. a volume of approximately 7.5 m3) or 1.5×2×3 m (i.e. a volume of approximately 9 m3). Accordingly, the container preferably has a volume of approximately 9 m3 or less, which is significantly less than the volume of a standard 20 ft ISO shipping container. The container may be pre-installed inside the transition piece to facilitate installation as mentioned above.
The switchgear components inside the container may be gas-insulated. Typically sulphur hexafluoride (SF6) gas is employed. The container may include a pressure-relief device for relieving pressure in the event of an overpressure within the container. The pressure relief device preferably comprises at least one pressure relief flap.
The wind turbine of the present invention preferably has a rating of 7.0 MW (megawatts) or above. The main transformer is preferably configured to increase the voltage from 3.3 kV to 33 kV or 66 kV. The first and second switching devices preferably have a rating of 630 A (Amperes) or 1250 A in a 36 kV arrangement or 1250 A or 2000 A in a 72 kV arrangement.
Within the same inventive concept, the present invention provides a wind power plant comprising a plurality of wind turbines as described above. The wind turbines are preferably connected together to form a collector grid. The connections to the collector grids are preferably made via the respective second switching devices, which may be configured to receive the respective incoming and outgoing grid cables.
Another advantage of containerised switchgear is that the container may be installed on an offshore wind turbine foundation prior to erecting the wind turbine. Often the foundations are built a year or more before the turbines are constructed, and so this conveniently allows the cables that interconnect the wind turbines in the collector grid to be tested before the wind turbines are erected. This results in increased efficiency and may reduce the time required to construct the wind power plant.
Accordingly, the invention also comprises a method of constructing an offshore wind power plant comprising: installing a plurality of offshore foundations in an array: providing containerised switchgear on each of the respective foundations; and connecting the containerised switchgear on the respective foundations to the containerised switchgear on another foundation in the array via electric cables prior to erecting wind turbines on the respective foundations. The method preferably comprises electrically testing the containerised switchgear and the interconnecting cables prior to erecting the wind turbines.
The method may further comprise erecting a wind turbine on a foundation: providing a switchgear component inside the wind turbine: and electrically connecting the switchgear component to the containerised switchgear on said foundation. The switchgear component inside the wind turbine may be installed after the tower has been erected on the foundation. Alternatively, the tower may be built around the switchgear component.
As a further alternative, the switchgear component may be pre-installed inside a section of the tower and the method may comprise transporting said section including the pre-installed switchgear component to the foundation for assembly with other tower sections to form the tower. The container may be pre-installed inside the transition piece. Pre-installing the switchgear equipment in this way facilitates installation because it dispenses with the requirement for separate offshore lifting processes to lift the switchgear equipment onto the foundation.
The switchgear component inside the wind turbine is preferably a circuit breaker or equivalent device configured to protect the electrical equipment of the wind turbine. The component is preferably connected between the main transformer of the wind turbine and the containerised switchgear outside the wind turbine. The switchgear component is preferably located adjacent the main transformer, for reasons that have already been described above. The method may advantageously comprise electrically connecting the switchgear component to the main transformer and testing the connected equipment as a combined unit prior to connecting the equipment with the other wind turbine equipment and with the containerised switchgear. These electrical tests may conveniently be performed offsite before the equipment is transported to the offshore foundation. The method may comprise pre-installing the transformer in a tower section together with the switchgear component prior to transporting the tower section to the foundation.
As the present invention relates broadly to the concept of separating the switchgear, the invention may also be expressed in terms of the switchgear without making direct reference to the wind turbine. Accordingly, the present invention also provides switchgear for location between a main transformer of a wind turbine and another wind turbine in a collector grid, the switchgear comprising a first switching device for associating with the main transformer, and a second switching device for associating with one or more cables connecting the wind turbine to the other wind turbine in the collector grid, wherein the first switching device is connected to, but located remotely from, the second switching device.